This invention pertains to exhaust gas recirculation (EGR) systems for internal combustion engines in automotive vehicles and particularly concerns a novel control system for exhaust gas recirculation.
EGR systems are currently utilized in many automobile engines for the purpose of reducing the amount of oxides of nitrogen in the engine exhaust. Basically, this is accomplished by allowing a controlled amount of hot exhaust as to recirculate and dilute the incoming fuel and air mixture. Typically, the EGR valve is a vacuum-actuated, poppet-type unit used to modulate exhaust gas flow from the exhaust gas crossover into the incoming air-fuel mixture. A common criticism of EGR systems in automobile engines is that driveability of the automobile is impaired under certain conditions and that fuel economy is significantly downgraded. Also, EGR systems are often complicated requiring extra components which add to the cost of the system and the complexity of the engine compartment. For example, where a high rate spring is used in the EGR valve it becomes necessary to use a vacuum amplifier unit for delivering the necessary amount of vacuum to overcome the high spring rate when the EGR valve is modulated.
The present invention is directed to a novel EGR control system which in certain respects reduces the amount of complexity otherwise required. According to the invention, a plurality of individual engine operational characteristics are monitored and utilized in determining when engine exhaust gas is to be recirculated. Broadly, in one aspect, the invention may be considered as providing an on-off (or "bang-bang" ) type of EGR system because the individual control signals developed from the monitored engine operational characteristics are utilized to either open or close a valve which is connected in a vacuum line between carburetor venturi vacuum tap and an EGR valve. In another aspect, the invention provides that the individual control signals are utilized in controlling exhaust gas recirculation such that all the control signals must be commanding exhaust gas recirculation for any exhaust gas recirculation to occur. Stated conversely, the control is such that if any one of the control signals is commanding no exhaust gas recirculation, then that signal overrides any other signals to the contrary so that no exhaust gas circulation occurs at all. A further aspect of the invention relates to the specific monitored engine operational characteristics which are utilized in controlling exhaust gas recirculation.
In a preferred embodiment of the present invention as hereinafter disclosed, a normally closed, solenoid-actuated valve is disposed in a vacuum line connecting carburetor venturi vaccum to an inlet control port of an EGR valve. Energization of the solenoid-actuated valve is controlled via an electrical control circuit which monitors a plurality of engine operational characteristics. These operational characteristics are: the amount of throttle blade opening; the magnitude of intake manifold vacuum; the relative durations of engine idle and non-idle operation during an immediately past time period; and the engine temperature. The electrical control circuit is so designed that all monitored characteristics must be commanding exhaust gas recirculation for the solenoid-actuated valve to be open. Thus, with this arrangement the EGR valve can be modulated by carburetor venturi vacuum only under a selected set of operating conditions; exhaust gas recirculation is terminated if any one or more of the monitored characteristics dictates that no exhaust gas is to be recirculated, whereby that characteristic effectively overrides any others which are to the contrary. From this description, it will be appreciated that in accordance with the invention, an engine powered automotive vehicle has a portion of its exhaust gas recirculated in a controlled on-off fashion by selected engine operating conditions. Satisfactory driveability, fuel economy, and compliance with emission target levels can be obtained with a lesser degree of complexity than in prior systems.
The foregoing features, advantages and benefits of the present invention will be seen in the ensuing description and claims which are to be considered in conjunction with the accompanying drawings.